Writing instrument



FIG. 1 is a front perspective view of an ornamental design of a writing instrument showing my new design;

FIG. 2 is a right side plan view thereof;

FIG. 3 is a left side plan view thereof;

FIG. 4 is a back side view thereof;

FIG. 5 is a front side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view.

The broken lines in the figures illustrate portions of the writing instrument that form no part of the claimed design. 

CLAIM I claim the ornamental design for a writing instrument, as shown and described. 